Seahorses aren’t odd simply for their horselike shape. They (and their syngnathid fish kin, seadragons and pipefish) are the only vertebrates in which the males take on the burden of pregnancy. You might think that since having pregnant guys is really weird, some keen scientists would have figured everything out about the phenomenon. But a lot of questions remain, in part because it doesn’t look the same in all species. In some, the seahorse brood pouch — the male alternative to the uterus — serves as a simple site for fertilized eggs to attach while they develop. In others, the eggs, after mom deposits them in the brood pouch, are fully enclosed and protected from the outside world.